Magnetic resonance imaging apparatus and image processing apparatus

ABSTRACT

A magnetic resonance imaging apparatus includes a first data acquisition unit, a second data acquisition unit and an image data generating unit. The first data acquisition unit acquires first data from a slice to be a target after a first delay time from a reference of a first heart rate in synchronization with an electrocardiogram. The second data acquisition unit acquires second data from the slice after a second delay time from a reference of a second heart rate which is different from the first heart rate. The image data generating unit generates image data with image reconstruction processing using the first data and the second data.

RELATED APPLICATION

This application is related to copending application Ser. No. 11/896,942filed Sep. 6, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic resonance imaging (MRI)apparatus and an image processing apparatus which excites nuclear spinsof an object magnetically with an RF (radio frequency) signal having theLarmor frequency and reconstructs an image based on an NMR (nuclearmagnetic resonance) signal generated due to the excitation, and moreparticularly, to a magnetic resonance imaging apparatus and an imageprocessing apparatus which can obtain a blood flow image in a shorterperiod of time without a contrast medium.

2. Description of the Related Art

Magnetic resonance imaging is an imaging method which excites nuclearspins of an object set in a static magnetic field with an RF signalhaving the Larmor frequency and reconstructs an image based on an NMRsignal generated due to the excitation.

MRA (Magnetic Resonance Angiography) is known as a technique forobtaining a blood flow image in the field of magnetic resonance imaging.MRA without using contrast medium is called a non-contrast-enhanced MRA.In non-contrast-enhanced MRA, a fresh blood imaging (FBI) method isdesigned, which clearly images a blood vessel by acquiring ahigh-velocity blood flow pumped out from the heart with ECG (electrocardiogram) synchronization (see, for example, Japanese PatentApplication (Laid-Open) No. 2000-5144).

A non-contrast-enhanced MRA image using the FBI method can obtain an MRAimage with arteriovenous separation by obtaining a difference betweenimage data acquired while varying delay time with ECG synchronization.Additionally, a Flow-Spoiled FBI method can be designed, whichsuppresses an artery signal during systole by applying a spoiler pulse.The Flow-Spoiled FBI method images a difference between artery signalsin diastole and systole of myocardium. An ECG-prep scan can be used todecide upon an optimum delay time for use with the ECG synchronization.

Furthermore, in the FBI method, a Flow-dephasing method can be designedin order to image a low-velocity blood flow, which applies a gradientpulse (Gspoil) in a readout (RO) direction and adds a dephasing pulse ora rephasing pulse to a gradient magnetic field pulse (see, for example,Japanese Patent Application (Laid-Open) No. 2002-200054, Japanese PatentApplication (Laid-Open) No. 2003-135430 and U.S. Pat. No. 6,801,800).The Flow-dephasing method can increase a relative signal differencebetween a high-velocity blood flow and a low-velocity blood flow byoperation of a dephasing pulse or a rephasing pulse. Then, the relativesignal difference allows one to more clearly separate arteries fromveins.

This means it is important to enlarge signal difference between diastoleand systole for clear arteriovenous separation. In order to do this, itis necessary to reduce signal intensity from high-velocity blood flow insystole. Therefore, a gradient pulse having an appropriate intensity inan RO direction is set and a blood flow signal from an artery in systoleis suppressed by the set gradient pulse. In this state, a blood flowsignal in diastole is acquired. Then, subtraction processing and/ormaximum intensity projection (MIP) processing is performed on the bloodflow signal acquired in diastole and thus only arteries are imaged.

The Flow-prep. Scan performs a preparation scan with changing parametersincluding intensity of a dephasing pulse in an RO direction in theFlow-dephasing method (see, for example, Japanese Patent Application(Laid-Open) No. 2003-70766). The Flow-prep. Scan makes it possible toobtain an optimum parameter by referencing images acquired with changedparameter values during the preparation scan. A research report aboutintensity of a dephasing pulse in an RO direction has been made (see,for example, Miyazaki M, et al., Radiology 227:890-896, 2003).

An echoshare technique with use of the Half-Fourier method is designedto obtain a blood flow image in a shorter scanning time (see, forexample, Japanese Patent Application (Laid-Open) No. 2001-149341). Scansin diastole and systole obtain pieces of data respectively by thistechnique. By the scan in systole, only echo data in a low-frequencyregion important for improving contrast is acquired in a short dataacquisition time. Instead, copies of data in a high-frequency regionacquired by the scan in diastole are used as data in the high-frequencyregion that are not acquired in systole. Moreover, if data is stillinsufficient in a region even with using a copy of data in diastole,then further data is calculated from K-space data for diastole andsystole by the Half-Fourier method so as to provide a complete K-spacedata set for image reconstruction.

A technique to obtain dynamic information of a blood flow simply withoutcontrast medium and measuring ECG-synchronization timing with anECG-prep scan can be designed (see, for example, Japanese PatentApplication (Laid-Open) No. 2004-329614). This technique uses anECG-prep scan as an imaging scan. Specifically, as in the case of anECG-prep scan, dynamic information of blood flow can be obtained byperforming subtraction processing on two-dimensional data acquired morethan once, but by imaging scans made at gradually changed respectivedelay times from an R wave of an ECG signal.

FIG. 18 is a diagram showing a conventional imaging scan with use of anECG-prep scan.

In FIG. 18, the abscissa denotes time. As shown in FIG. 18, a triggersignal is set initially at a timing of delay time d1 from an R wave ofan ECG signal. Then, a scan for data acquisition is started insynchronization with the trigger signal. Then, a trigger signal is setat a delay time d2 from an R wave of the ECG signal after completion ofthe scan for data acquisition. Then, a scan for data acquisition isstarted in synchronization with the trigger signal. In the same way,trigger signals are set at delay times d3, d4, . . . from R waves of theECG signal respectively, and a scan for data acquisition is started at adifferent timing in synchronization with each trigger signal. At thistime, delay times d1, d2, . . . are set to be changed gradually insystole of a myocardium showing a great change in velocity of bloodflow.

A pulse sequence that consists of a two-dimensional partial FS (flowspoiling) pulse and/or a two-dimensional partial FC (flow compensation)pulse is used as a data acquisition scan.

The imaging scan as shown in FIG. 18 can reconstruct multiple pieces(i.e., sets) of image data each corresponding to a mutually differentdelay time from an R wave of the ECG signal.

FIG. 19 is a diagram showing delay times from an R wave of an ECG signalfor respective acquisition timings of pieces of image data acquired bythe imaging scan shown in FIG. 18.

In FIG. 19, the abscissa denotes time and each arrow denotes a timing ofan R wave of an ECG signal. As shown in FIG. 19, multiple pieces ofimage data each corresponding to a mutually different delay time from anR wave of the ECG signal are generated by an imaging scan. This meansmultiple pieces of image data each corresponding to a mutually differentcardiac time phase are generated. A subtraction image obtained byperforming subtraction processing to the pieces of image data generatedin this way becomes a blood flow image presenting dynamic information ofa blood flow. This blood flow image is called the Time-resolved MRDSA(magnetic resonance digital subtraction angiography) image since it is asubtraction image of a blood flow resolved by time.

A technique can also be designed to obtain dynamic information of bloodflow mentioned above by PI (parallel imaging) which is one of theavailable high speed imaging methods. PI is a technique for using a PAC(phased array coil) having surface coils as an RF coil for datareception (see, for example, Japanese Patent Application (Laid-Open) No.2004-329613). By using PI for obtaining dynamic information of bloodflow, Ran scanning time can be reduced.

In a conventional technique for obtaining a Time-resolved MRDSA image,data acquisition time per 1 shot to acquire Time-resolved MRDSA dataused for generating a Time-resolved MRDSA image is considerably longcompared to typical intervals between R waves. Therefore, a TR(repetition time) is set to be about 3RR corresponding to 3 times of adistance RR between R waves.

Consequently, an imaging time of about 60 to 90 seconds is necessary togenerate different Time-resolved MRDSA images corresponding to 20 to 30time phases. Therefore, shortening of imaging time is needed.

In addition to shortening of imaging time, when scanned data isprocessed simply and appropriately in accordance with the diagnosticpurpose and a user can refer to a diagnostic image more easily, workingtime and diagnostic time of the user can be reduced even if an imagingtime might increase.

SUMMARY OF THE INVENTION

The present invention has been made in light of the conventionalsituations, and it is an object of the present invention to provide amagnetic resonance imaging apparatus and an image processing apparatuswhich make it possible to perform imaging such as non-contrast-enhancedMRA with a shorter imaging time.

Furthermore, another object of the present invention is to provide amagnetic resonance imaging apparatus and an image processing apparatuswhich make it possible to display a diagnostic image, such as an MRAimage, appropriate for diagnosis with an easier operation by a user.

The magnetic resonance imaging apparatus and the image processingapparatus as described above make it possible to perform imaging such asnon-contrast-enhanced MRA with a shorter imaging time.

Further, the magnetic resonance imaging apparatus and the imageprocessing apparatus as described above make it possible to display adiagnostic image, such as an MRA image, appropriate for diagnosis withan easier operation by a user.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing a magnetic resonance imaging apparatusaccording to an embodiment of the present invention;

FIG. 2 is a diagram showing an example of detail structure of the RFcoil shown in FIG. 1;

FIG. 3 is a sectional illustration showing an example arrangement of theWB coil and the phased array coils shown in FIG. 2;

FIG. 4 is a functional block diagram of the computer shown in FIG. 1;

FIG. 5 is a flowchart showing a procedure for acquiring a non-contrastTime-resolved MRDSA image of the object with the magnetic resonanceimaging apparatus shown in FIG. 1;

FIG. 6 is a diagram showing an example of setting window displayed as auser interface on the monitor shown in FIG. 1;

FIG. 7 is a diagram showing delay times for data acquisitions and dataacquisition periods in case of selecting the echo share mode on thesetting window shown in FIG. 6;

FIG. 8 is a diagram showing relation between pieces of data acquired bythe data acquisition shown in FIG. 7;

FIG. 9 is a diagram showing an FASE sequence used as a sequence for thedata acquisition shown in FIG. 7;

FIG. 10 is a diagram showing a sequence obtained by adding Partial FCpulses to the FASE sequence shown in FIG. 9;

FIG. 11 is a diagram showing a sequence obtained by adding Partial FSpulses to the FASE sequence shown in FIG. 9;

FIG. 12 is a diagram explaining effect and how to set each intensity ofthe Partial FC pulse and the Partial FS pulse shown in FIGS. 10 and 11respectively;

FIG. 13 is a diagram showing k-space data obtained in case of performingdata acquisition with the FASE sequence shown in FIG. 9;

FIG. 14 is a diagram showing delay times and data acquisition periods incase of performing data acquisition for selecting the echo share mode onthe setting window shown in FIG. 6 and generating a three-dimensionalTime-resolved MRDSA image by a three-dimensional pulse sequence;

FIG. 15 is a diagram explaining an order for displaying MIP images whichis set on the setting window shown in FIG. 6;

FIG. 16 is a diagram explaining a method for displaying pieces of bloodflow image data corresponding to two parts respectively with matchingtime phases when the pieces of blood flow image data are obtained withmoving the bed 37;

FIG. 17 is a diagram explaining a method for displaying image data ofupstream side corresponding to the last time phase and subsequentlyimage data of the adjacent downstream side corresponding to the firsttime phase according to a direction of blood flow when the pieces ofblood flow image data corresponding to two parts respectively areobtained with moving the bed;

FIG. 18 is a diagram showing a conventional imaging scan with use of anECG-prep scan; and

FIG. 19 is a diagram showing delay times from an R wave of an ECG signalfor respective acquisition timings of pieces of image data acquired bythe imaging scan shown in FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A magnetic resonance imaging apparatus and an image processing apparatusaccording to embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a block diagram showing a magnetic resonance imaging apparatusaccording to an embodiment of the present invention.

A magnetic resonance imaging apparatus 20 includes a static field magnet21 for generating a static magnetic field, a shim coil 22 arrangedinside the static field magnet 21 which is cylinder-shaped, a gradientcoil unit 23 and a RF coil 24. The static field magnet 21, the shim coil22, the gradient coil unit 23 and the RF coil 24 are built in a gantry(not shown).

The magnetic resonance imaging apparatus 20 also includes a controlsystem 25. The control system 25 includes a static magnetic field powersupply 26, a gradient power supply 27, a shim coil power supply 28, atransmitter 29, a receiver 30, a sequence controller 31 and a computer32. The gradient power supply 27 of the control system 25 includes anX-axis gradient power supply 27 x, a Y-axis gradient power supply 27 yand a Z-axis gradient power supply 27 z. The computer 32 includes aninput device 33, a monitor 34, a operation unit 35 and a storage unit36.

The static field magnet 21 communicates with the static magnetic fieldpower supply 26. The static magnetic field power supply 26 supplieselectric current to the static field magnet 21 to get the function togenerate a static magnetic field in a imaging region. The static fieldmagnet 21 includes a superconductivity coil in many cases. The staticfield magnet 21 gets current from the static magnetic field power supply26 which communicates with the static field magnet 21 at excitation.However, once excitation has been made, the static field magnet 21 isusually isolated from the static magnetic field power supply 26. Thestatic field magnet 21 may include a permanent magnet which makes thestatic magnetic field power supply 26 unnecessary.

The static field magnet 21 has the cylinder-shaped shim coil 22coaxially inside itself. The shim coil 22 communicates with the shimcoil power supply 28. The shim coil power supply 28 supplies current tothe shim coil 22 so that the static magnetic field becomes uniform.

The gradient coil unit 23 includes an X-axis gradient coil unit 23 x, aY-axis gradient coil unit 23 y and a Z-axis gradient coil unit 23 z.Each of the X-axis gradient coil unit 23 x, the Y-axis gradient coilunit 23 y and the Z-axis gradient coil unit 23 z which iscylinder-shaped is arranged inside the static field magnet 21. Thegradient coil unit 23 has also a bed 37 in the area formed inside itwhich is an imaging area. The bed 37 supports an object P. Around thebed 37 or the object P, the RF coil 24 may be arranged instead of beingbuilt in the gantry.

The gradient coil unit 23 communicates with the gradient power supply27. The X-axis gradient coil unit 23 x, the Y-axis gradient coil unit 23y and the Z-axis gradient coil unit 23 z of the gradient coil unit 23communicate with the X-axis gradient power supply 27 x, the Y-axisgradient power supply 27 y and the Z-axis gradient power supply 27 z ofthe gradient power supply 27 respectively.

The X-axis gradient power supply 27 x, the Y-axis gradient power supply27 y and the Z-axis gradient power supply 27 z supply currents to theX-axis gradient coil unit 23 x, the Y-axis gradient coil unit 23 y andthe Z-axis gradient coil unit 23 z respectively so as to generategradient magnetic fields Gx, Gy and Gz in the X, Y and Z directions inthe imaging area.

The RF coil 24 communicates with the transmitter 29 and the receiver 30.The RF coil 24 has a function to transmit a RF signal given from thetransmitter 29 to the object P and receive an NMR signal generated dueto nuclear spin inside the object P which is excited by the RF signal togive to the receiver 30.

FIG. 2 is a diagram showing an example of detail structure of the RFcoil 24 shown in FIG. 1. FIG. 3 is a sectional illustration showing anexample arrangement of the WB coil 24 a and the phased array coils 24 bshown in FIG. 2.

The RF coil 24 is structured by a transmission RF coil 24 and areception RF coil 24, for example. The transmission RF coil 24 uses awhole-body (WB) coil 24 a while the reception RF coil 24 uses a phasedarray coil 24 b. The phased array coil 24 b has a plurality of surfacecoils 24 c. The surface coils 24 c are separately connected torespective reception circuits 30 a.

Meanwhile, the surface coils 24 c of the phased array coil 24 b arearranged, symmetric about the Z-axis, in peripheral regions of a sectionL including a particular region of interest in the object P for example.Furthermore, the WB coil 24 a is provided at the outer of the phasedarray coil 24 b. Thus, a radio frequency signal can be transmitted tothe object P by the WB coil 24 a while an NMR signal of from the sectionL including the particular region of interest can be received atmulti-channels by the WB coil 24 a or the surface coils 24 c of thephased array coil 24 b and provided to the reception circuits 30 a ofthe receiver 30.

However, the RF coil 24 may be structured by desired coils suited forvarious applications or by a single coil.

The sequence controller 31 of the control system 25 communicates withthe gradient power supply 27, the transmitter 29 and the receiver 30.The sequence controller 31 has a function to storage sequenceinformation describing control information needed in order to make thegradient power supply 27, the transmitter 29 and the receiver 30 driveand generate gradient magnetic fields Gx, Gy and Gz in the X, Y and Zdirections and a RF signal by driving the gradient power supply 27, thetransmitter 29 and the receiver 30 according to a predetermined sequencestored. The control information above-described includes motion controlinformation, such as intensity, impression period and impression timingof the pulse electric current which should be impressed to the gradientpower supply 27

The sequence controller 31 is also configured to give raw data to thecomputer 32. The raw data is complex number data obtained through thedetection of an NMR signal and A/D conversion to the NMR signal detectedin the receiver 30.

The transmitter 29 has a function to give a RF signal to the RF coil 24in accordance with control information provided from the sequencecontroller 31. The receiver 30 has a function to generate raw data whichis digitized complex number data by detecting a NMR signal given fromthe RF coil 24 and performing predetermined signal processing and A/Dconverting to the NMR signal detected. The receiver 30 also has afunction to give the generated raw data to the sequence controller 31.

In addition, an ECG unit 38 for acquiring an ECG signal of the object Pis provided with the magnetic resonance imaging apparatus 20. The ECGsignal detected by the ECG unit 38 is outputted to the computer 32through the sequence controller 31.

Furthermore, the bed 37 is provided with a table drive unit 39. Thetable drive unit 39 is connected with the computer 32 so as to move thetable of the bed 37 under the control by the computer 32 for imagingwith moving table method or stepping table method. The moving tablemethod is a technique for obtaining a large FOV (field of view) in amoving direction by continuously moving the table of the bed 37 duringimaging. The stepping table method is a technique for three-dimensionalimaging at every station by stepping the table of the bed 37. Thesetechniques are used in case of imaging a large area which is unable tobe imaged at a time such as whole body imaging. The images acquired withmoving the bed 37 may be combined mutually by compound processing in thecomputer 32.

The computer 32 gets various functions by the operation unit 35executing some programs stored in the storage unit 36 of the computer32. Alternatively, some functions may be provided with the magneticresonance imaging apparatus 20 by some specific circuits instead ofusing some of the programs.

FIG. 4 is a functional block diagram of the computer 32 shown in FIG. 1.

The computer 32 functions as a sensitivity distribution database 40, aninterface unit 41, an imaging condition setting unit 42, a sequencecontroller control unit 43, a k-space database 44, an imagereconstruction unit 45, an unfolding processing unit 46, a real spacedatabase 47, a blood flow image generating unit 48, a display processingunit 49 and a table control unit 50 by program.

The sensitivity distribution database 40 stores each sensitivitydistribution of the surface coils 24 c included in the phased array coil24 b.

The interface unit 41 has a function to display a window for setting andinputting various information on the display unit 34 with the GUI(Graphical User Interface) technology and a function to receiveinstruction from the input device 33 and provide it to correspondingcomponents. Information such as an imaging condition, an imageprocessing method and an image displaying method can be cited as setinformation.

Sequences for non-contrast MRA each to be set as an imaging conditionincludes two-dimensional or three-dimensional FSE (Fast spin echo)sequence, EPI (echo planar imaging) sequence, FASE (fast asymmetric spinecho) sequence and SSFP (steady state free precession) sequence. Usingtwo-dimensional sequence make it possible to reduce imaging period.Further, in case of using two-dimensional FASE sequence, a Partial FSpulse or a Partial FC pulse for controlling a phase of magnetized spinmay be added to a gradient magnetic field pulse in a RO (readout)direction according to a blood velocity.

An FASE sequence with applying a partial FC pulse is suitable forimaging a portion such as a vessel with a high-velocity blood flow. Whenimaging a portion showing a low-velocity blood flow, an FASE sequencewith applying a flow spoiling pulse, an EPI sequence or an SSFP sequencecan be used. Since an SSFP sequence has a long TE (echo time) and issensitive to a flow, it can depict a flow-void image in a systole and/ora bright blood image in a diastole.

Further, a delay time from an R wave of an ECG signal and the number ofdata acquisition (the number of shots) are set as imaging conditions togenerate a Time-resolved MRDSA image. For example, each delay time canbe set as a delay time until the first data acquisition, i.e., aninitial value of the delay time and an increment value indicating anamount of change of the delay time.

The set imaging conditions including the pulse sequence, the delay timeand the number of shots are output from the interface unit 41 to theimaging condition setting unit 42 and the image reconstruction unit 45.

In addition, an imaging mode with the echoshare and/or an imaging modeunder PI can be selected as an imaging condition for generating aTime-resolved MRDSA image. Imaging with the echoshare acquires only echodata in a low-frequency region critical for improvement of contrast in ashort data acquisition time in a scan in a systole and uses a copy ofdata in a high-frequency region acquired in a scan in a diastole as datain the high-frequency region that was not acquired in the systole.

PI receives data with multiple surface coils 24 c and reduces the numberof phase encodes into a value obtained by multiplying the reciprocal ofthe number of the surface coil 24 c with the number of phase encodesnecessary for image reconstruction by skipping at least one phaseencode. When the imaging mode under PI is selected, conditions specificto PI are also set. As conditions specific to PI, the number of thesurface coil 24 c used as a receiver coil and a ratio for expanding aFOV for unfolding processing, which is post-processing to image dataobtained by PI, so that the FOV for unfolding processing becomes largerthan that set at the time of an imaging plan in order to prevent foldingpossibly occurred in PI, are cited. The number of the surface coil 24 cis also called the speeding-up rate.

When the imaging mode with echoshare is selected, instruction to set animaging condition with echoshare is provided from the interface unit 41to the image condition setting unit 42, and instruction to perform imagereconstruction processing with echoshare together with necessary imagingcondition information is provided from the interface unit 41 to theimage reconstruction unit 45.

When the imaging mode under PI is selected, instruction to set animaging condition for PI is provided from the interface unit 41 to theimage condition setting unit 42. Further, information that a target ofreconstruction processing is each piece of K-space data, acquired by PI,from the respective surface coils 24 c is provided from the interfaceunit 41 to the image reconstruction unit 45, and a condition for PI isprovided from the interface unit 41 to the unfolding processing unit 46then used for unfolding processing.

Moreover, when imaging by the moving table method or the stepping-tablemethod, instruction to set conditions including a position of the bed 37and an amount of step is provided from the interface unit 41 to theimage condition setting unit 42 as imaging conditions.

As image processing methods, instruction indicating whether to generatea blood flow image by automatically performing traction processing toreconstructed image data and/or instruction indicating whether toautomatically perform projection processing such as MIP (maximumintensity projection) processing when a blood flow image isthree-dimensional can be made. Instruction indicating automaticsubtraction processing and/or automatic projection processing isprovided from the interface unit 41 to the blood flow image generatingunit 48.

In addition, as an image displaying method, when a blood flow image iseach of time series projection images obtained by projection processing,conditions including a projecting direction, a display order and adisplay speed of the projection images can be appointed. The swing/phasedisplay that displays multiple projection images while swinging adirection of projection and subsequently displays the projection imagesof the next phase, and inversely, the phase/swing display that displaysmultiple projection images while swinging the phase and subsequentlydisplays the projection images swung in another direction are cited as adisplay order. However, only projection images projected in a constantdirection can be displayed dynamically as an image displaying method.

When the swing/phase display or the phase/swing display is instructedthrough operation of the input device 33, instruction of projectionimages that should be generated is provided to the blood flow imagegenerating unit 48, and a display order and/or a display speed ofgenerated projection images are provided as instruction to the displayprocessing unit 49, respectively from the interface unit 41.

When imaging by the moving table method or the stepping-table method,since multiple pieces of imaging data are obtained on every position ofthe bed 37, a displaying method of the imaging data at every position ofthe bed 37 can be specified. Instruction of the displaying method of theimaging data at every position of the bed 37 is provided from theinterface unit 41 to the display processing unit 49.

The imaging condition setting unit 42 has a function to set imagingconditions including a pulse sequence according to instruction obtainedfrom the input device 33 through the interface unit 41 and provide theset imaging conditions to the sequence controller control unit 43. Whenimaging by the moving table method or the stepping-table method, theimaging condition setting unit 42 is configured to provide controlinformation of the bed 37 according to the imaging conditions to thetable control unit 50.

The sequence controller control unit 43 has a function for controllingthe driving of the sequence controller 31 by giving imaging conditioninformation indicating imaging conditions including a pulse sequenceobtained from the imaging condition setting unit 42 to the sequencecontroller 31 based on indication of starting a scan obtained from theinput device 33 through the interface unit 41 or another element.Further, the sequence controller control unit 43 has a function forreceiving raw data, which is k-space (Fourier space) data, from thesequence controller 31 and arranging the raw data to k space formed inthe k-space database 44.

The k-space database 44 stores the k-space data received from thesequence controller control unit 43.

The image reconstruction unit 45 has a function for capturing thek-space data from the k-space database 44, generating image data fromthe k-space data by performing image reconstruction processing, such asFourier transform processing to the k-space data, and writing thegenerated image data to the real space database 47. In addition, theimage reconstruction unit 45 is configured to perform imagereconstruction processing with echoshare according to instruction andimaging conditions when the instruction to perform image reconstructionprocessing with echoshare and the imaging conditions is provided fromthe interface unit 41.

Further, the image reconstruction unit 45 is also configured to providepieces of image data from the respective surface coils 24 c obtained byimaging with PI to the unfolding processing unit 46. Information aboutwhether the imaging conditions include imaging under PI or not isprovided through the interface unit 41 from the input device 33 to theimage reconstruction unit 45.

The unfolding processing unit 46 has a function to generate unfoldedimage data by performing unfolding process, which is post-processing inPI, to image date from each surface coil 24 c obtained from the imagereconstruction unit 45 in accordance with the conditions for PI acquiredfrom the interface unit 41 and also to write the generated image data inthe real space database 47. The unfolding processing unit 46 isconfigured to be able to refer to the sensitivity distribution of eachsurface coil 24 c stored in the sensitivity distribution database 40 forunfolding processing.

The real space database 47 stores image data generated by the imagereconstruction unit 45 or the unfolding processing unit 46.

The blood flow image generating unit 48 has a function to acquiremultiple pieces of image data each corresponding to a mutually differentcardiac time phase stored in the real space database 47 to generateblood flow image data for displaying according to instruction from theinterface unit 41. For example, by subtraction processing between piecesof image data each corresponding to a mutually near time phase orbetween reference image data and image data corresponding to each timephase, two-dimensional or three-dimensional Time-resolved MRDSA imagedata can be generated. Furthermore, blood flow image data for displayingcan be generated by performing necessary image processing such as MIPprocessing in a predetermined direction to the Time-resolved MRDSA imagedata according to instruction from the interface unit 41. Note that, itis acceptable to consider image data in each time phase as blood flowimage data for displaying without subtraction processing to image data.

The Blood flow image data such as two-dimensional Time-resolved MRDSAimage data and projection image data finally generated for displaying isprovided from the blood flow image generating unit 48 to the displayprocessing unit 49.

The display processing unit 49 has a function to output the blood flowimage data acquired from the blood flow image generating unit 48 on thedisplay unit 34 at the displaying order and the displaying speedinstructed by the interface unit 41. When imaging by the moving tablemethod and the stepping-table method, the display processing unit 49 isconfigured to obtain the positional information of the bed 37 from thetable control unit 50 and output blood flow image data, corresponding toeach position of the bed 37, on the display unit 34 according to thedisplaying method instructed by the interface unit 41.

The table control unit 50 has a function to provide the positionalinformation of the bed 37 to the table drive unit 39 to control thetable drive unit 39 so that the bed 37 can drive according to thecontrol information of the bed 37 depending on the imaging conditionsprovided by the imaging condition setting unit 42, and to provide thepositional information of the bed 37 to the display processing unit 49.

Then, the operation and action of the magnetic resonance imagingapparatus 20 will be described.

FIG. 5 is a flowchart showing a procedure for acquiring a non-contrastTime-resolved MRDSA image of the object P with the magnetic resonanceimaging apparatus 20 shown in FIG. 1. The symbols including S with anumber in FIG. 5 indicate each step of the flowchart.

In step S1, instruction of whether to apply echoshare and PI as imagingconditions for acquiring a non-contrast-enhanced Time-resolved MRDSAimage is provided. For that purpose, window information is provided fromthe interface unit 41 to the display unit 34, and a setting window toset information including an imaging condition, an image processingcondition, an image displaying condition and the like is displayed onthe display unit 34.

FIG. 6 is a diagram showing an example of setting window displayed as auser interface on the monitor 34 shown in FIG. 1.

For example, a setting window to set an imaging condition, an imageprocessing condition and an image displaying condition is displayed onthe display unit 34 as shown in FIG. 6. The imaging mode with echoshareand/or the imaging mode under PI can be selected respectively as animaging condition. FIG. 6 shows an example in which both of theechoshare mode and the PI mode are selected. Since the PI mode isselected, the number of the surface coil 24 c and a No Wrap valueindicating a scale for enlarging a FOV for unfolding processing toprevent folding are set respectively. FIG. 6 shows an example in whichthe number of the surface coil 24 c for data acquisition is 4 and the NoWrap value is 1.5.

A pulse sequence for a non-contrast-enhanced MRA can be selected frompreset candidates. FIG. 6 shows an example in which a two-dimensionalFASE sequence is selected. Since data acquisition for anon-contrast-enhanced Time-resolved MRDSA image is performed over pluraltimes with extending a delay time from an R wave of an ECG signalgradually, each delay time and the number of data acquisition, i.e., thenumber of shots are set. In FIG. 6, an initial delay time from an R wavefor the first data acquisition and an increment value equivalent to anincrement of a delay time for the following data acquisition are set to100 ms and 5 ms, respectively. In addition, the number of shots is setto 30.

As shown in FIG. 6, “NUMBER OF PHASES” instead of “NUMBER OF SHOTS” maybe displayed since a single shot sequence such as an FASE sequence whichis an FSE sequence with using half Fourier method may be used.

When the imaging mode with echoshare is selected, the K-space data fromthe low-frequency region to the high-frequency region necessary forreconstruction of a slice of Time-resolved MRDSA image is acquired atleast once, and an imaging condition is set so that only K-space data ofthe low-frequency region including data that is at least necessary forensuring contrast is acquired in other data acquisition. The range ofK-space data to be acquired in the low-frequency region can bedetermined by imaging on a trial basis in advance and determiningwhether the contrast can be sufficiently obtained or not.

For this reason, in the imaging mode with echoshare, the dataacquisition time for acquiring the only K-space data in thelow-frequency region can be decreased. Preferably, an imaging conditionis set so that the K-space data in the low-frequency region is acquiredbetween consecutive R waves of an ECG signal, i.e., in one heart beat.More preferably, an imaging condition is set so that a time necessaryfor a longitudinal relaxation (T1) recovery can be secured between theend of data acquisition and the next R wave.

From the viewpoint that the data acquisition time is made shorter andthat the data in the high-frequency region is acquired as higher signalvalues, the data in the high-frequency region is acquired in the lastdata acquisition with the longest delay time for practical purposes. Acase where the data from the low-frequency region to the high-frequencyregion is acquired only once in the last data acquisition is describedhere.

FIG. 7 is a diagram showing delay times for data acquisitions and dataacquisition periods in case of selecting the echo share mode on thesetting window shown in FIG. 6.

As shown in FIG. 7, the data acquisition time is reduced since the dataonly in the low-frequency region is acquired in each data acquisitionother than the last data acquisition of nth. When an FASE sequenceobtained by combining the fast SE method with the Half-Fourier method isselected as a sequence for the data acquisition, the data acquisitiontime can be reduced further and the data in the low-frequency region canbe acquired in one heart beat.

Therefore, triggers can be set at timings of delay times d1, d2, d3, . .. , dn from R waves of an ECG signal respectively, and the data can beacquired continuously.

FIG. 8 is a diagram showing relation between pieces of data acquired bythe data acquisition shown in FIG. 7.

In FIG. 8, the abscissa denotes time and each arrow denotes a timing ofan R wave of an ECG signal. By the data acquisition as shown in FIG. 7,multiple pieces of K-space data corresponding to mutually differentdelay times from R waves of the ECG signal as shown in FIG. 8 can beacquired. Since the nth K-space data includes both data in thelow-frequency region and the high-frequency region, it has a data sizelarger than that of the K-space data acquired with another delay time.The image data can be generated from multiple pieces of K-space datacorresponding to mutually different cardiac time phases as describedabove. Furthermore, a subtraction image obtained by subtractionprocessing to the generated pieces of image data becomes a Time-resolvedMRDSA image that represents a dynamic state of a blood flow.

FIG. 9 is a diagram showing an FASE sequence used as a sequence for thedata acquisition shown in FIG. 7.

In FIG. 9, RF denotes RF signals to be transmitted, Gs denotes agradient magnetic field for slice selection, Gr denotes a gradientmagnetic field for readout, Ge denotes a gradient magnetic field forphase encode and ECHO denotes acquired echo data.

As shown in FIG. 9, following a 90 degrees excitation pulse P90, a 180degrees refocus pulse P180 is continuously applied to an object P as anRF signal. In addition, gradient magnetic fields Gs, Gr, Ge for sliceselection, for readout and for phase encoding are applied to the objectP. In each data acquisition other than nth one, an RF signal andgradient magnetic fields are applied to the object P so that only echodata in the low-frequency region can be acquired. On the contrary, inthe nth data acquisition, an RF signal and gradient magnetic fields areapplied to the object P so that echo data in the high-frequency regionas well as the low-frequency region can be acquired. Consequently, datain the center of K-space is acquired after the effective echo timeTEeff.

A partial FC pulse and/or a partial FS pulse can be applied along with agradient magnetic field pulse for readout depending on a velocity of ablood flow. Since a partial FC pulse and a partial FS pulse have afunction to control a phase of magnetization spin, they can be called aphase behavioral control pulse.

FIG. 10 is a diagram showing a sequence obtained by adding Partial FCpulses to the FASE sequence shown in FIG. 9.

In FIG. 10, RF denotes RF signals to be transmitted, Gs denotes agradient magnetic field for slice selection, Gr denotes a gradientmagnetic field for readout, Ge denotes a gradient magnetic field forphase encode and ECHO denotes acquired echo data.

As shown in FIG. 10, a partial FC pulse Pfc is applied before and aftera gradient magnetic field pulse for readout in the direction of thereverse polarity. The waveform area of the partial FC pulse Pfc is setto larger than 0% and smaller than 100% of that of the gradient magneticfield pulse for readout depending on a velocity of a blood flow. Then,by the operation of the partial FC pulse Pfc applied before the gradientmagnetic field pulse for readout, phase dispersion of the magnetizationspin is suppressed and thus the signal value can be acquired withoutfail. The partial FC pulse Pfc applied after the gradient magnetic fieldpulse for readout has a role to compensate the phase of themagnetization spin. For this reason, when a blood flow velocity is highand a signal value is low, the use of an FASE sequence with applying apartial FC pulse Pfc for imaging is effective.

FIG. 11 is a diagram showing a sequence obtained by adding Partial FSpulses to the FASE sequence shown in FIG. 9.

In FIG. 11, RF denotes RF signals to be transmitted, Gs denotes agradient magnetic field for slice selection, Gr denotes a gradientmagnetic field for readout, Ge denotes a gradient magnetic field forphase encode and ECHO denotes acquired echo data.

As shown in FIG. 11, a partial FS pulse Pfs is applied before and aftera gradient magnetic field pulse for readout in the direction of thereverse polarity. The waveform area of the partial FS pulse Pfs is setto larger than 0% and smaller than 100% of that of the gradient magneticfield pulse for readout depending on a velocity of a blood flow. Then,by the operation of the partial FS pulse Pfs applied before the gradientmagnetic field pulse for readout, phase dispersion of the magnetizationspin is promoted and thus a high signal value can be acquired. Thepartial FS pulse Pfs applied after the gradient magnetic field pulse forreadout has a role to compensate the phase of the magnetization spin.For this reason, when a blood flow velocity is low, the use of an FASEsequence with applying a partial FS pulse Pfs for imaging is effective.

FIG. 12 is a diagram explaining effect and how to set each intensity ofthe Partial FC pulse and the Partial FS pulse shown in FIGS. 10 and 11respectively.

In FIG. 12, the ordinate denotes a blood velocity and relative signalvalue, and the abscissa denotes time from an R wave of an ECG signal.Further in FIG. 12, the dashed line denotes a temporal variation ofblood velocity and the dotted line denotes a temporal variation ofsignal value of data acquired from a blood flow by an FASE sequence.

As shown in FIG. 12, in the systole before a time t1, although thevelocity of the blood flow is relatively fast, the signal intensityobtained from the blood flow is relatively small. Meanwhile, in thediastole after the time t2, although the velocity of the blood flow isrelatively slow, the signal intensity obtained from the blood flow isrelatively high. This means a signal intensity varies depending on atime from an R wave of an ECG signal.

When a partial FC pulse and/or a partial FS pulse are applied, phasedispersion of magnetization spin is suppressed or promoted, and thus atime variation of a signal value changes. For example, the timevariation S1 of the signal value shown as a solid line changes into thetime variation S2 of the signal value shown as a dotted line. In otherwords, adjusting intensity of a partial FC pulse and/or a partial FSpulse can control a signal value obtained from a blood flow.Consequently, when a partial FC pulse and/or a partial FS pulse areapplied with changing their intensity every one shot depending on avelocity of a blood flow and/or a delay time, each piece of data can beacquired in equivalent signal intensity at a different cardiac timephase.

Each intensity (or each waveform area) of a partial FC pulse and apartial FS pulse can be determined for every imaging portion byacquiring data on a trial basis in advance. It is acceptable to displayeach intensity of a partial FC pulse or a partial FS pulse determined asa default on a setting window of the display unit 34 once, and to enablea user to change it arbitrarily through operation of the input device33.

When K-space data is acquired by a pulse sequence like this, theacquired K-space data, except for data by the last data acquisition ofnth that acquires data in the low-frequency region and thehigh-frequency region, becomes data only in the low-frequency region.

FIG. 13 is a diagram showing k-space data obtained in case of performingdata acquisition with the FASE sequence shown in FIG. 9.

In FIG. 13, the abscissa denotes an RO direction and the ordinatedenotes a PE direction. The K-space data as shown in FIG. 13 is acquiredper one shot. Since the Half-Fourier method is used in an FASE sequence,the K-space data of a high-frequency region in the positive direction isnot acquired. The K-space data of a low-frequency region in the positivedirection is acquired by the data acquisition until the effective echotime TEeff and the K-space data of a low-frequency region in thenegative direction is acquired by the data acquisition after theeffective echo time TEeff.

The copy of the data, of a high-frequency region, acquired by the nthdata acquisition is used as the K-space data of a high-frequency regionin the negative direction that is necessary for image reconstruction butis not acquired.

This means the K-space data of a low-frequency region critical for theimprovement of contrast is acquired per heart beat, and the K-space dataof a high-frequency region is acquired at least once then shared betweenpieces of data acquired in the respective shots.

As described above, the number kn of lines of the K-space data in a PEdirection can be determined as the number making it possible to obtainenough contrast by a test of imaging in advance. Alternatively, a rangeof K-space data to be acquired may be displayed on a setting window ofthe display unit 34 so that a user can change it through operation ofthe input device 33.

An example of setting an imaging condition for a two-dimensionalTime-resolved MRDSA image has been described so far. However, theimaging condition for the two-dimensional Time-resolved MRDSA image canbe used as an imaging condition of an ECG-prep scan that is apreparation scan for acquiring an optimum delay time from an R wave ofan ECG signal.

When an ECG-prep scan is performed, a signal value of data from a bloodflow per delay time from an R wave can be acquired. Consequently, agraph relating the delay times to the signal values of the data can bedisplayed so that a range of delay times for imaging an MRDSA image andthe number of time phases (delay times) can be determined with referenceto the graph. A graph relating the delay times to the signal values ofdata can be generated according to the following procedure (algorithm).

First, multiple ECG-prep images each corresponding to a mutuallydifferent delay time are generated by an ECG-prep scan. Any one of themultiple ECG-prep images is assumed to be the reference image, and thena difference between each ECG-prep image and the reference image isobtained. Alternatively a difference between two ECG-prep images out ofmultiple ECG-prep images is obtained with regard to all combinations.This generates multiple subtraction images. Then, an MIP image isgenerated by MIP processing to multiple subtraction images. Then, a maskimage is generated by binarizing the MIP image and subsequently thegenerated mask image is multiplied by each of the multiple ECG-prepimages. This enables an amount of characteristic regarding each delaytime (time phase) to be calculated. Then, a graph relating each delaytime to the amount of characteristic calculated in this way can begenerated.

When a graph relating delay times to signal values of data is displayedfor setting of imaging conditions and/or display conditions, theinterface unit 41 is configured to obtain necessary data from anothercomponent such as the real space database 47, generate graph informationexpressing the graph relating the graph information on the display unit34. Further, a graph range is specified through operation of the inputdevice 33, and then the interface unit 41 provides instruction of animaging range and/or a display range based on the specified graph rangeto the imaging condition setting unit 42 and the display processing unit49.

By referencing the graph, a range of delay times for imaging an MRDSAimage can be specified. For example, an imaging range can be set in atime phase, with signal variation, from a systole to a diastole of aheart. Specifically, an imaging range can be regarded as a range inwhich a delay time from an R wave of an ECG signal is from 200 ms to 350ms.

Moreover, in addition to an imaging range, a variation width of a delaytime and/or a repetition frequency of data acquisition also becometargets for setting as mentioned above. FIG. 6 shows an example ofsetting window that specifies an initial value of a delay time, avariation width of the delay time and a frequency of data acquisitionthrough operation of the input device 33. However, a variation width ofa delay time and/or a repetition frequency of data acquisition may becalculated automatically by the computer 32 according to conditions. Forexample, if a range of delay times for imaging is specified, byspecifying a reference delay time (an initial value of a delay time, forexample) Delay and a variation width Increment of a delay time throughoperation of the input device 33, the computer 32 can automaticallycalculate a repetition frequency of data acquisition and an imagingtime. For another example, when an imaging time is specified throughoperation of the input device 33, the computer 32 can automaticallycalculate a reference delay time Delay and a variation width Incrementof a delay time so that the data acquisition of the specified imagingrange is completed within the specified imaging time. The repetitionfrequency of data acquisition, the imaging time, the reference delaytime Delay and the variation width Increment of the delay time, obtainedby these calculations or specified, can be displayed on the display unit34 for reference.

Note that, since an ECG-prep scan is a preparation scan performed todetermine an appropriate delay time, a variation width of a delay timefor an MRDSA image is ordinarily set shorter than that betweenrespective pieces of image data obtained by the ECG-prep scan.

Further, when a graph relating delay times concerning an MRDSA image tosignal values of data is displayed, a range of delay times and thenumber of time phases (delay times) for displaying a blood flow imagecan also be determined.

Meanwhile, an imaging condition with echoshare for imaging athree-dimensional Time-resolved MRDSA image can also be set.

FIG. 14 is a diagram showing delay times and data acquisition periods incase of performing data acquisition for selecting the echo share mode onthe setting window shown in FIG. 6 and generating a three-dimensionalTime-resolved MRDSA image by a three-dimensional pulse sequence.

As shown in FIG. 14, data acquisition at a slice S1 can be performedsimilarly to two-dimensional data acquisition shown in FIG. 7.Specifically, data in the high-frequency region and the low-frequencyregion in the last data acquisition of nth at the slice S1 is acquiredwhile data only in the low-frequency region is acquired in the otherdata acquisition. In a similar way, three-dimensional data can beacquired by two-dimensional data acquisition with echoshare repeated forevery slice. In other words, each data acquisition for the slices S2,S3, . . . , Sn is performed similarly to the data acquisition for theslice S1. This allows to acquire three-dimensional echo data in a shorttime and generate a three-dimensional Time-resolved MRDSA image.

An imaging time can be reduced by selecting the echoshare mode asmentioned above on a setting window of an imaging condition.

Moreover, when the imaging mode by PI is selected on a setting window ofan imaging condition, an imaging time can be reduced further. PI is atechnique for acquiring data by skipping at least one phase encode withmultiple surface coils 24 c as described above. Therefore, the number ofphase encodes can be reduced to a value obtained by multiplying areciprocal of the number of surface coils 24 c by the number of a phaseencodes necessary for image reconstruction. Then, pieces of image datacorresponding to the respective surface coils 24 c are reconstructedfrom pieces of echo data received simultaneously by the respectivesurface coil 24 c.

However, folding occurs in each piece of reconstructed image data forthe respective surface coils 24 c by PI. Therefore, unfolding processingis performed to each of the respective pieces of image data to removefolding by utilizing each sensitivity distribution of the surface coils24 c. Then conclusive image data for displaying is generated bycombining the pieces of image data for the respective surface coils 24 cafter unfolding processing.

When imaging by moving table method or stepping-table method,instruction to set a condition such as positional information and anamount of step of the bed 37 is provided from the input device 33 to theinterface unit 41 as an imaging condition.

When the instruction of the imaging condition as mentioned above isprovided from the input device 33 to the interface unit 41 through thesetting window displayed on the display unit 34, the correspondinginformation is provided form the interface unit 41 to the respectivecomponents. For example, application information of the echoshare modeand/or PI, the number of the surface coil 24 c, the selected pulsesequence, the delay time and the number of shots are provided to theimaging condition setting unit 42. Further, application information ofthe echoshare mode, the pulse sequence, the delay time, the number ofshots and application information of PI are provided to the imagereconstruction unit 45, and application information of PI and the numberof the surface coil 24 c are provided to the unfolding processing unit46, respectively.

Then, the image condition setting unit 42 sets imaging conditionsaccording to the information obtained from the interface unit 41 andprovides them to the sequence controller control unit 43.

Next in the step S2, an image processing method and an image displayingmethod are set through a setting window of an image processing conditionand an image displaying condition displayed on the display unit 34. Asshown in the upper right portion in FIG. 6, the auto subtractionprocessing mode serving as an image processing method can be selected soas to perform subtraction processing automatically for generating anMRDSA image. When selecting the auto subtraction mode, subtractionprocessing between pieces of image data is performed automatically togenerate an MRDSA image without additionally providing instruction ofsubtraction processing to the interface unit 41 after the beginning ofimaging.

For example, when a three-dimensional sequence is selected as a pulsesequence for data acquisition, the auto-MIP processing mode can beselected so as to perform MIP processing automatically. If the auto-MIPprocessing mode is selected, MIP processing to three-dimensional imagedata generated as MRDSA data is performed automatically to generateblood flow image data for displaying without providing instruction ofMIP processing to the interface unit 41 separately after the beginningof imaging.

In addition, when a three-dimensional sequence is selected as a pulsesequence for data acquisition, a displaying method of multiple pieces ofMIP image data generated as blood flow image data for displaying can beset as shown in the lower right portion in FIG. 6.

FIG. 15 is a diagram explaining an order for displaying MIP images whichis set on the setting window shown in FIG. 6.

In FIG. 15, the abscissa denotes a display angle representing aprojection direction for MIP images and the ordinate denotes time phase.The images laid out as shown in FIG. 15 are MIP images for displayingacquired by a three-dimensional scan. In FIG. 15, a display angle of anMIP image changes toward in the abscissa axis direction, and the timeelapses and blood on an MIP image flows gradually toward in the ordinateaxis direction.

When Phase/Swing is selected as an image displaying method, the MIPimages are displayed on the display unit 34 in the image display methodfor displaying MIP images corresponding to mutually different timephases sequentially, and subsequently displaying MIP images from anotherdisplay angle with elapse of time phase sequentially after.Specifically, the MIP images are displayed on the display unit 34 in theorder of Ip1 a 1, Ip2 a 1, Ip3 a 1, . . . , Ip1 a 2, Ip2 a 2, Ip3 a 2, .. . , Ip1 a 3, Ip2 a 3, Ip3 a 3, . . . . On the other hand, whenSwing/Phase is selected as an image displaying method, the MIP imagesare displayed on the display unit 34 in the image displaying method fordisplaying MIP images with gradually changing a display anglesequentially, and subsequently displaying MIP images in the next timephase with gradually changing a display angle. Specifically, the MIPimages are displayed on the display unit 34 in the order of Ip1 a 1, Ip1a 2, Ip1 a 3, . . . , Ip2 a 1, Ip2 a 2, Ip2 a 3, . . . , Ip3 a 1, Ip3 a2, Ip3 a 3, . . . .

In addition, a direction of projection for generating an MIP image canbe set as an image displaying method. For example, the number ofprojection directions can be specified and projection planes obtained byevenly dividing the angle of 180 degrees by the specified number can beset as the projection direction. Moreover, a displaying time of one MIPimage can be set. For example, when the scroll bar is scrolled to theminus side in FIG. 6, a displaying speed of MIP images slows down andthe MIP images are displayed in slow motion. On the contrary, when thescroll bar is scrolled to the plus side, the MIP images are run withfast-forward.

In addition, when imaging by the moving table method or thestepping-table method, an image displaying method of a blood flow imagedata can be set according to each position of the bed 37. In this casein connection with an image displaying method, when an imaging conditionis set so that mutually corresponding pieces of data between pluralportions serving as imaging targets in positions of the bed 37 areacquired with the same delay time, blood flow image data can bedisplayed effectively.

For example, when blood flow image data is for a moving image, the bloodflow image data can be displayed with matching time phases betweenpieces of blood flow image data from respective positions.

FIG. 16 is a diagram explaining a method for displaying pieces of bloodflow image data corresponding to two parts respectively with matchingtime phases when the pieces of blood flow image data are obtained withmoving the bed 37.

As shown in FIG. 16, two pieces of blood flow image data can beconnected and displayed in the time series. When time phases d1, d2, d3,. . . of the respective pieces of blood flow image data I1 and I2 aremutually set to be same or near, the blood flow image data can bedisplayed as if blood is flowing in each of the blood flow images I1 d1, I1 d 2, I1 d 3, . . . , I2 d 1, I2 d 2, I2 d 3, . . . .

FIG. 17 is a diagram explaining a method for displaying image data ofupstream side corresponding to the last time phase and subsequentlyimage data of the adjacent downstream side corresponding to the firsttime phase according to a direction of blood flow when the pieces ofblood flow image data corresponding to two parts respectively areobtained with moving the bed 37.

As shown in FIG. 17, two pieces of blood flow image data I1 and I2 canbe connected and displayed in the time series. When displaying thedownstream blood flow image data I2 d 1 corresponding to the initialtime phase d1 after displaying the upstream blood flow image data I1 d 3corresponding to the last time phase d3, the blood flow image data canbe displayed as if blood is flowing continuously between two parts.

Information indicating an image displaying method and an imageprocessing method that are thus set up is provided from the interfaceunit 41 to the blood flow image generating unit 48 as a blood flow imageto be generated, and information indicating the image displaying methodis also provided to the display processing unit 49.

After completing setting of the imaging condition, the image processingmethod and the image displaying method, an object P is set on the bed37. Further, a static magnetic field is generated in an imaging area inthe static field magnet 21 (superconducting magnet) excited in advanceby the static magnetic field power supply 26. An electric current issupplied from the shim coil power supply 28 to the shim coil 22 touniform the static magnetic field generated in the imaging area. Theimaging condition, the image processing method and the image displayingmethod may be set collectively, not separately.

Then in step S3, data acquisition is performed. Specifically,instruction to start a scan is provided through the interface unit 41from the input device 33 to the sequence controller control unit 43.Then, the sequence controller control unit 43 provides a pulse sequencesuch as an FASE sequence acquired from the imaging condition settingunit 42 to the sequence controller 31. The sequence controller 31generates a gradient magnetic field in the imaging area where the objectP is set by driving the gradient power supply 27, the transmitter 29 andthe receiver 30 according to the pulse sequence received from thesequence controller control unit 43 and also generates a radio frequencysignal from the RF coil 24.

Consequently, an NMR signal generated by the nuclear magnetic resonancein the object P is received by the RF coil 24 and provided to thereceiver 30. The receiver 30 performs necessary signal processing inresponse to the NMR signal from the RF coil 24, and then generates rawdata that is an NMR signal of digital data by A/D conversion. Thereceiver 30 provides the generated raw data to the sequence controller31. The sequence controller 31 provides the raw data to the sequencecontroller control unit 43 and the sequence controller control unit 43arranges the raw data as K-space data in the K-space formed in theK-space database 44.

The data acquisition like this is performed in synchronization with anECG according to an ECG signal of the object P acquired by the ECG unit38. That is to say, following triggers set so as to increase a delaytime gradually from an R wave of the ECG signal, pieces of datacorresponding to the number of shots specified through the settingwindow shown in the FIG. 6 are acquired. The delay time increases by theincrement value, depending on the number of shots, from the initialdelay time set in the setting window in the FIG. 6.

In the echoshare mode, K-space data of a low-frequency region isacquired in each shot other than the nth shot and arranged in theK-space database 44 while K-space data of a low-frequency region and ahigh-frequency region is acquired in the nth shot and arranged in theK-space database 44. Therefore, the data can be acquired in a short timeand data for one shot can be acquired in one heart beat. When theimaging mode by PI is selected, since data is acquired by the specifiednumber of the surface coils 24 c with skipping the number of phaseencodes, data acquisition time is reduced further. Consequently,sufficient time can be reserved for T1 recovery between the end of dataacquisition and the next R wave.

Then in step S4, the image reconstruction unit 45 generates image datafrom K-space by retrieving the K-space data from the K-space database 44and performing image reconstruction processing such as Fourier transformprocessing to the K-space data. Note that, a copy of the K-space data ofthe high-frequency region acquired in the nth data acquisition is usedas deficient K-space data, of the high-frequency region in the K-spacein the negative direction, among the K-space data acquired in each dataacquisition other than nth. Further, the deficient K-space data of thehigh-frequency region in the positive direction in the K-space iscalculated based on the complex conjugate relation under theHalf-Fourier method. When the K-space is filled with the copy of dataand by the complex conjugate calculation, the image data is generated byimage reconstruction processing.

When a notice of the imaging mode by PI from the interface unit 41 isnot provided, the image reconstruction unit 45 writes the image dataobtained by reconstruction on the real space database 47. On thecontrary, when a notice of the imaging mode by PI from the interfaceunit 41 is provided, the image reconstruction unit 45 provides thepieces of image data, corresponding to the respective surface coils 24c, obtained by reconstruction to the unfolding processing unit 46.

The unfolding processing unit 46 generates unfolded image data byperforming unfolding processing on the image data from each surface coil24 c obtained from the image reconstruction unit 45. At this time, eachsensitivity distribution of corresponding surface coils 24 c stored inthe sensitivity distribution database 40 is referred to by the unfoldingprocessing unit 46 and used for unfolding processing. In addition, acondition such as the number of the surface coils 24 c and NOWRAPobtained from the interface unit 41 is also used for unfoldingprocessing. Then, the unfolding processing unit 46 writes the generatedimage data on the real space database 47.

Then in step S5, according to the instruction from the interface unit41, the blood flow image generating unit 48 obtains multiple pieces ofimage data corresponding to mutually different cardiac time phasesstored in the real space database 47 and generates blood flow image datafor displaying. For example, the blood flow image generating unit 48generates Time-resolved MRDSA image data by subtraction processingbetween pieces of image data corresponding to mutually near time phaseor between a reference image data and image data corresponding to eachtime phase.

When performing subtraction processing of the image data in each timephase to the reference image data, a timing corresponding to a delaytime dn from an R wave of the ECG signal is set in a diastole and imagedata acquired in the diastole can be considered to be the referenceimage data Idn. When performing subtraction processing between the imagedata Id1, Id2, Id3, . . . in each time phase, acquired at a timingcorresponding to each delay time d1, d2, d3, . . . , and the referenceimage data Idn, subtraction image data Idn-Id1, Idn-Id2, Idn-Id3, . . .obtained as a result of subtraction processing becomes bright cine imagedata showing blood flow images.

This subtraction processing is performed automatically when the autosubtraction processing mode is selected in the setting window shown inthe FIG. 6. On the contrary, when the auto subtraction processing modeis not selected, a user operates the input device 33 so that instructionof subtraction processing is provided to the blood flow image generatingunit 48 through the interface unit 41.

Alternatively, the image data Id1, Id2, Id3, in each time phase may beset as blood flow image data for displaying without subtractionprocessing, as it is. In this case, the blood flow image data fordisplaying becomes black cine image data.

When acquisition of two-dimensional image data for an ECG-prep is thepurpose, no subtraction processing of time-resolved data is alsonecessary and therefore the image data generated by the imagereconstruction unit 45 or the unfolding processing unit 46 can be usedwithout modification.

When the auto-MIP processing mode is selected in the setting windowshown in the FIG. 6, the three-dimensional Time-resolved MRDSA imagedata after subtraction processing is automatically subjected to MIPprocessing toward a specified projection plane.

The two-dimensional Time-resolved MRDSA image data and the MIP imagedata generated by this means are provided as blood flow image data fromthe blood flow image generating unit 48 to the display processing unit49.

Then in step S6, the display processing unit 49 performs displayprocessing to the blood flow image data according to the instructionfrom the interface unit 41 so that the blood flow image data can bedisplayed on the display unit 34 in the displaying order and thedisplaying time set in the setting window, and outputs the processedblood flow image data to the display unit 34. As a result, a blood flowimage is displayed on the display unit 34. When the three-dimensionalTime-resolved MRDSA image data is especially generated, multiple MIPimages are sequentially displayed in a displaying method instructed asPhase/Swing or Swing/Phase.

When imaging by the moving table method or the stepping-table method hasbeen performed, pieces of blood flow image data corresponding to therespective positions of the bed 37 are mutually connected. Therespective pieces of blood flow image data can be displayed withmatching their time phases, and alternatively can be displayedcontinuously so that the initial time phase in the downstream side cancome after the last time phase in the upstream side.

That is to say, the magnetic resonance imaging apparatus 20 as mentionedabove is an apparatus which can acquire data in a short time using theechoshare technique and/or PI so that image data of a single slice andmulti phases can be acquired effectively. The image data of a singleslice and multi phases is aimed at non-contrast-enhanced Time-resolvedMRDSA image data and image data acquired by an ECG-prep.

According to the echoshare technique, it is only necessary to performdata acquisition of only low-frequency components in the K-space severaltimes, and perform data acquisition of high-frequency components in theK-space at least once. This can reduce an imaging time per shot.Moreover, an imaging time can be reduced further in combination with PI.Consequently, data can be acquired with a TR as one heart beat (1RR). Itis suitable to use an FASE sequence that can acquire data in a shortertime. At this time, data can be acquired with a stable signal value byapplying a Partial FC pulse and/or a Partial FS pulse according to avelocity of a blood flow.

Furthermore, if the echoshare technique and/or PI are applied to athree-dimensional non-contrast-enhanced Time-resolved MRDSA,three-dimensional blood flow function, which is DSA information in aslice direction, can be measured in a short time. Consequently,according to the magnetic resonance imaging apparatus 20, imaging ofnon-contrast-enhanced Time-resolved MRDSA image as functional imagingcan be performed in a shorter time.

In addition, configuration of an interface so that subtractionprocessing and/or MIP processing are automatically performed to thereconstructed image data can reduce work of a user. At the same time, byproviding with an interface in consideration of user's convenience, anMIP image in each time phase and to each projection direction can beautomatically and sequentially displayed in a displaying order and adisplaying speed specified in advance without the user's operation whenMIP images are generated in multiple directions by three-dimensionalimaging. This continuous automatic display of MIP images in time seriestoward multiple projection directions can be performed on blood flowimages with contrast medium and/or images other than blood flow imagesas well as on non-contrast-enhanced blood flow images. An interface canbe configured so that auto subtraction processing and/or automaticprojection processing can be performed in a three-dimensionalTime-resolve MRDSA without the echoshare technique and/or PI.

Moreover, with the echoshare technique, a method of generating an imageusing pieces of data acquired in a certain heart beat and in anotherheart beat respectively can also be used for generating not only anon-contrast-enhanced blood flow image but a blood flow image withcontrast medium and a diagnostic image other than a blood flow image. Incombination with PI, this method can be applied to generation of variousdiagnostic images including a non-contrast-enhanced blood flow image anda blood flow image with contrast medium as well.

Meanwhile, the magnetic resonance imaging apparatus 20 as mentionedabove generates image data in the state where K-space data is filled byusing a copy of K-space data in a high-frequency region according to theechoshare technique and performs subtraction processing of the generatedimage data. However, the magnetic resonance imaging apparatus 20 canalso generate image data once from K-space data consisting of onlylow-frequency components for subtraction processing and performcomplementary processing, as display processing, of a part correspondingto a high-frequency component to subtraction image data acquired asblood flow image data before displaying the subtraction image data. Inthis case, complementary processing to the blood flow image data can beperformed by the display processing unit 49. In this way, when a copy ofa high-frequency component is used as complementary data aftersubtraction processing, blood flow image data can be also obtained withhigh resolution.

In addition, an image processing apparatus can be configured to haveimage processing functions, such as the subtraction processing andprojection processing, of the magnetic resonance imaging apparatus 20 asmentioned above and representational function of various image data. Animage processing apparatus can be built in a PACS (picture archiving andcommunication system) for example, and can connect to the magneticresonance imaging apparatus 20 via networks. In this case, part of theimage processing function and/or the representational processingfunction can be omitted from the magnetic resonance imaging apparatus20. However, if both of the magnetic resonance imaging apparatus 20 andthe image processing apparatus have the image processing function andthe representational processing function, a blood flow image can bedisplayed as a moving image or a still image in a various displayingmethod on both of the magnetic resonance imaging apparatus 20 and theimage processing apparatus.

What is claimed is:
 1. A magnetic resonance imaging (MRI) apparatuscomprising: an assembly of MRI gantry components including static andgradient magnetic field generators and at least one radio frequency (RF)coil defining an imaging volume; an MRI control system, connected tocontrol said gantry components, including at least one RF transmitter,at least one RF receiver and computer control circuits connected toeffect specified MRI data acquisition sequences of RF and gradientmagnetic pulses which acquire, from an object located within saidimaging volume, RF nuclear magnetic resonance (NMR) spin responsesemanating from different spatially located volumes of NMR nucleirespectively corresponding to different positions in k-space as afunction of a magnetic field experienced by the nuclei; said computercontrol circuits being connected to: acquire three or morenon-contrast-enhanced MRA image data sets from a region to be imaged atthree or more respectively corresponding different delay times insynchronization with an electrocardiogram, wherein each of the three ormore corresponding different delay times is set using an initial valueof a delay time from an R-wave and a further increment valuerepresenting a change in delay times; and reconstruct an acquired threeor more non-contrast-enhanced MRA image data sets to generatetime-resolved MRDSA (Magnetic Resonance Digital Subtraction Angiography)images representing a dynamic state of blood flow, wherein a k-spacedata set which includes both k-space data in a low-frequency region andk-space data in a high-frequency region is acquired only for one imagedata set of the three or more non-contrast-enhanced MRA image data sets,the one image data set corresponding to a longest delay time of thethree or more corresponding different delay times, wherein k-space datasets which include k-space data only in a low-frequency region areacquired for all other image data sets of the three or more non-contrastenhanced MRA image data sets, the other image data sets corresponding todelay times other than the longest delay time, and wherein the three ormore non-contrast-enhanced MRA image data sets are reconstructed aftercopying the k-space data in the high-frequency region acquired at thelongest delay time into a high-frequency region of each of the k-spacedata sets acquired at delay times other than the longest delay time. 2.The magnetic resonance imaging apparatus of claim 1, wherein thecomputer control circuits are further configured to acquire the three ormore non-contrast-enhanced MRA image data sets under an imagingcondition having a time necessary for longitudinal relaxation recoveryis between an end of data acquisition and a next R wave.
 3. The magneticresonance imaging apparatus of claim 1, wherein the computer controlcircuits are further configured to acquire data in the center of k-spaceafter an effective echo time.
 4. The magnetic resonance imagingapparatus of claim 3, further comprising: a monitor, wherein thecomputer control circuits are further configured to set an imageprocessing condition using an input window displayed on the monitor andto thereafter automatically perform a subtraction processing.
 5. Themagnetic resonance imaging apparatus of claim 1, further comprising: asubtraction processing unit configured to generate subtraction imagedata by performing subtraction processing to the three or morenon-contrast-enhanced MRA image data sets.
 6. The magnetic resonanceimaging apparatus of claim 5, further comprising: a monitor, wherein thecomputer control circuits are further configured to set an imageprocessing condition using an input window displayed on the monitor andto thereafter automatically perform a subtraction processing.
 7. Themagnetic resonance imaging apparatus of claim 1, wherein the computercontrol circuit is further configured to: generate subtraction imagedata as non-contrast-enhanced time-resolved magnetic resonance digitalsubtraction angiography (MRDSA) image data by performing subtractionprocessing to the three or more non-contrast-enhanced MRA image datasets.
 8. The magnetic resonance imaging apparatus of claim 1, wherein aportion of an entire region in k-space for delay times other than thelongest delay time is a low spatial frequency region of k-space whichimproves contrast in the time-resolved MRDSA (Magnetic Resonance DigitalSubtraction Angiography) images.
 9. The magnetic resonance imagingapparatus of claim 1, wherein the computer control circuits are furtherconfigured to acquire the data sets sequentially with gradually changeddelay times.
 10. The magnetic resonance imaging apparatus of claim 1,wherein the computer control circuits are further configured to acquiredata sets using a fast asymmetric spin echo (FASE) sequence.
 11. Themagnetic resonance imaging apparatus of claim 1, wherein the computercontrol circuits are further configured to acquire data sets using afast asymmetric spin echo (FASE) sequence in which a phase behavioralcontrol pulse for controlling phases of magnetized spins is added to agradient magnetic field pulse for readout, the phase behavioral controlpulse being applied with an intensity depending on at least one of (a) ablood flow velocity and (b) a delay time.
 12. The magnetic resonanceimaging apparatus of claim 1, wherein the computer control circuits arefurther configured to acquire data sets three-dimensionally from pluralslices, and to generate three-dimensional image data.
 13. The magneticresonance imaging apparatus of claim 1, further comprising pluralreception coils to acquire the three or more non-contrast enhanced MRAimage data sets while skipping at least one phase encode period, andwherein the computer control circuits are further configured to performunfolding processing which removes a fold arising in a plural image datasets based on sensitivity distributions of a plural reception coils.